<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>灯泡开关</title>
</head>
<body>
  <script>
    function fn(n) {
      return Math.floor(Math.sqrt(n + 0.5));
    }
    console.log(fn(3))
  </script>
</body>
</html>